Weed control in rice with metham-sodium.

Metam-sodium is a soil fumigant with herbicidal properties. A field experiment was conducted in 2000 at Copiano (Pavia, Italy) to determine the efficacy of three rates of metam-sodium (300, 450 and 600 l/ha) at three different planting times (5, 12 and 18 days after chemical treatments) for the control of weeds in rice cultivation. The study mainly focused on the control of red rice (Oryza sativa var. selvatica), a weed which is worldwide distributed in rice fields and difficult to eradicate Test design was a split-plot with four replications. The main plot size was 13, 5 by 15 m and the subplot size was 13, 5 by 5 m. The chemical treatments were carried out as pre-sowing. Two days after chemical treatments, all field plots were flooded with 10 cm of water as practiced locally. An early variety of rice (Loto) was sown at 150 kg/ha. Weed control was visually evaluated as a percentage of ground covering by all weeds and by each weed individually at three, four and five weeks after treatments. Observations were made also on rice selectivity, and rice grain yield was assessed at the end. Metam-sodium did not injure the rice plants. Metam-sodium at 450 l/ha controlled 100%, 97% and 92% of red rice at the first, second and third observations, respectively. Good results were also obtained with metam-sodium at 300 and 600 l/ha, which controlled 94 to 82% of red rice during the season. Echinochloa crus-galli was better controlled with the higher rates of metam-sodium, particularly in the early part of the season. Metam-sodium did not show enough efficacy in this study against Heteranthera reniformis, Bulboschoenus maritimus and Lindernia spp. The best rice grain yield was obtained with all rates of metam-sodium, when rice was sown 5 days after treatment.